Radon Reporter March 2022

THE RADON REPORTER | 17 MITIGATION owner placed a Radon Eye under a 5-liter bowl sealed against the slab or foundation wall using plumber putty (Figure 1). Note that the oil in plumber putty will stain concrete. Exposure during the first 12 hours usually provides the best straight line of increasing radon; longer exposures have a flattening radon curve. It is helpful to plot the results on a spreadsheet to identify the most consistent rise of radon levels. Flux bucket radon level change is divided by hours of the change to calculate pCi ingrowth per hour. Ingrowth per hour is multiplied by the bowl volume in liters minus the volume of the CRM. This result is divided by the slab ft 2 area the bowl covers to obtain the pCi/ ft 2 /Hr result. If the flux is assumed to be the same across the slab, the result is then multiplied by the area of the basement slab and the same for the foundation wall area. The sum of these is the total amount of radon entering the basement per hour from concrete, which is then divided by the number of liters of ventilation entering the basement per hour. Unless the basement ventilation rate is measured, an assumed air change per hour (ACH) must be used. Current ventilation standards recommend about 0.35 air changes ACH. Basements tend to have much less, especially in new, well-insulated homes. The owner also reported lower basement radon levels in the winter than in the summer, which happens if the radon source is steady, but ventilation increases. Winter stack effect tends to increase basement ventilation (ACH) and cause lower radon levels if the radon source is steady. A variable is the run time of a basement-located air handler which may run more in the winter than summer and raise or lower radon levels. In this house, the HVAC running continuously reduced the radon levels by about 40%. The concrete total radon contribution is divided by the volume of 0.05 ACH to indicate an 8.05 pCi/l contribution of basement radon from concrete flux (Figure 2). Two tests were used to determine the basement natural ventilation rate to size a Heat Recovery Ventilator (HRV). One test requires turning off the radon system, and after the new radon level is reached, turn the system on and measure the time it takes to return to the radon system running. The other more definitive test is to introduce a measured amount of air from the outside into the basement and measure the new radon level. In both tests, it is necessary to establish a steady baseline radon level and a steady modified radon level. For this simple ventilation test, the radon fan was turned off until radon levels plateaued, and then the fan was turned back on. It is best to keep HVAC off for this test. Determine the ventilation rate by counting the number of hours it takes to double or halve the radon levels. The rough ACH estimate is 1 divided by the number of hours it took to halve the radon levels. This test indicated 0.05 ACH (Figure 2). The rising radon level may take longer because the system depleted the ground source. For the next test, a basement window was replaced with cardboard and a radon fan was connected to a flexible duct routed through the window cardboard. The fan airflow measured 100 CFM with the flex duct wide open and 50 CFM with a restricting cap (Figure 3). The natural FIGURE 2